This period has also been marked by the exploration of novel strategies to control the emission, propagation and confinement of light with nanostructures – a discipline nowadays known as “nanophotonics” [1]}. Research has been greatly stimulated by advances in nanofabrication techniques, which enabled the realization of a large variety of dielectric and metallic subwavelength structures with nanometer-scale resolution, in one, two and three dimensions [2]}, [3]}. One major outcome has been to unveil the potential of finely-engineered high-index resonant nano-objects to exhibit exotic properties, such as a light bending effect [4]}, a strong scattering anisotropy [5]} or a side-dependent coupling to waveguides [6]}. By optimizing the composition, size and shape of the nano-objects and placing them on a substrate, one creates a so-called “metasurface” that can deviate, focus, or alter the polarization state of an incident beam. The topic has become extremely popular and is covered by many review and expert opinion articles [7]}, [8]}, [9]}, [10]}.
